This invention relates to a variable capacity vane compressor which has variable compression starting timing to thereby control the delivery quantity or capacity of the compressor.
A variable capacity vane compressor for use in air conditioners for automotive vehicles has been proposed by Japanese Provisional Patent Publication (Kokai) No. 63-16186 assigned to the assignee of the present application, which has a control element having a high pressure chamber defined therein for creating control pressure from discharge pressure, the control element being rotatable in opposite directions in response to the difference between the control pressure and suction pressure from a suction chamber to assume a partial capacity position and a full capacity position for varying the compression starting timing and hence the capacity of the compressor, a control valve device arranged to establish communication between the high pressure chamber and the suction chamber for permitting the control pressure to leak from the former into the latter, the control valve device having a bellows expanding and contracting in response to change in the suction pressure in accordance with a thermal load, and a spool valve having a spool as a valve body responsive to the bellows for displacement between a valve opening position and a valve closing position, and wherein the valve control device controls the control pressure to control the angular position of the control element so as to bring the suction pressure to a predetermined value. In addition, a compressor having a ball valve in place of the spool valve has also been proposed by the same assignee.
The proposed compressors are adapted to control the capacity thereof so as to bring the suction pressure to the predetermined value (Internal Control). Such variable capacity compressors may be further controlled in capacity by an external control signal by means of electronic control means. To control the capacity by the external control signal, an electromagnetic valve may be used in place of the above-mentioned control valve device using bellows to vary the angular position of the control element.
However, in the case where the control valve device is formed of a bellows and a ball valve, if the bellows is replaced by an electromagnetic valve, a large electromagnetic force has to be applied upon the ball valve to open the valve to counteract the control pressure which is high pressure and usually acts upon the ball valve in a direction closing the valve. However, it is impossible to mount in the compressor an electromagnetic valve which is so large in capacity and hence size as to overcome the valve opening pressure of the ball valve.
On the other hand, in the case where the control valve device is formed of a bellows and a spool valve, if the bellows is replaced by an electromagnetic valve, the spool valve can be arranged such that the spool thereof has opposite end faces both acted upon by the suction pressure and is thus balanced in pressure. Therefore, the spool can be positively displaced in a valve opening direction even by a small force applied by the electromagnetic valve.